True love involves commitment and intimacy, which friendships can have, but it also involves romantic attraction. You are sexually attracted to this person. They make the butterflies in your stomach go wild and release chemicals in your brain that make you want to do anything for them. This is a sign of love.
Even though passion wanes after the honeymoon stage, a great relationship will still have passion.
However, some friendships can be sexual. We all know friends with benefits, where friends can have sex with each other but still have no strings attached, theoretically speaking. However, these relationships tend to lack commitment and while there may be an intimate connection, it is not as strong as love would be.